As silver halides for photographic light-sensitive materials, crystals of silver iodide, silver bromide or silver chloride and mixed crystals thereof are known and as the shapes of the silver halide crystal grains in an emulsion which contains the grains as precipitated and formed in a protective colloid, various kinds of crystal shapes are known including so-called regular grains such as cubic, tetradecahedral, octahedral or rhombic dodecahedral grains and irregular grains such as tabular grains or the like and also spherical and other amorphous grains whose crystal faces could hardly be specified by their appearances. Further, other crystal grains having a multiphase structure or junction structure inside the grain are known. The shapes of the silver halide crystal grains, as well as the halogen compositions and the structures thereof, would largely determine various properties of the grains and additionally would be important factors for determining the characteristics of silver halide photographic light-sensitive materials using the emulsions containing the crystal grains.
Silver halide emulsions form grains of different shapes depending upon their halogen compositions or upon the conditions under which the crystal grains are formed. For instance, E. Moisar and E. Klein reported in Berichte der Bunsengesellschaft fur Physikalische Chemie, 67, 949 (1963) that cubic, tetradecahedral or octadecahedral silver halide grains could be obtained by what is known as a double jet method where the excess amount of bromide ion is kept at a low value or at a high value during the addition of the silver salt and the halide salt in the formation of the grains. In addition, C. R. Berry, S. J. Marino and C. F. Oster reported in Photographic Science and Engineering, 5, 332 (1961) that similar crystal grains could be obtained by controlling the Ag value in the presence of ammonia. They further reported that the elevation of the pAg value in the absence of ammonia resulted in the formation of tabular grains with twin planes. Moreover, there are a number of reports in literature other than the above, mentioning so-called multiphase twin crystal grains having double phase or more multiphase twin planes. For instance, D. C. Skillman and C. R. Berry reported multiphase twin crystal grains in Photographic Science and Engineering, 6, 159 (1962) and ibid., 8, 65 (1964).
It is well known that silver iodobromide grains having silver iodide in some degree can also be formed almost in the same manner as the formation of the above-mentioned silver bromide grains. In addition, it is further known that silver chlorobromide grains having silver chloride can also be formed almost in the same manner, provided that the content of the silver chloride is not as high as the content of silver iodide in the above-mentioned silver iodobromide grains.
The same does not always hold, however, when the content of the silver chloride is high. It is difficult, for example, to form octahedral grains of silver chloride by regulation of the silver ion concentration. On the contrary, it is known that silver chloride or silver chlorobromide having a large content of silver chloride would often form cubic grains. However, some silver chloride or silver chlorobromide grains are known to be able to have some other shapes than cubic shape. For instance, West German Patent Publication No. 2,222,297 illustrates silver chloride or silver chlorobromide grains with a (110) crystal face or rhombic dodecahedral crystal grains. F. H. Claes, J. Libeer and W. Vanassche in The Journal of Photographic Science, 21, 39 (1973) report the formation of silver chloride crystals of rhombic dodecahedral grains with a (110) crystal face or of octahedral grains with a (111) crystal face by the use of various kinds of modifying agents. U.S. Pat. Nos. 4,399,215, 4,400,463 and 4,414,306 illustrate tabular grains with a (111) main crystal face of silver chloride or silver chlorobromide having a relatively high content of silver chloride. U.S. Pat. No. 4,386,156 illustrates tabular grains with a (100) main crystal face. Many of these silver halide crystals having various shapes, but not all of them are actually used in silver halide photographic materials in the form of an emulsion containing the grains singly or in the form of a mixture of different grains. It is well known that the silver halide crystal grains as contained in the emulsion of photographic materials display the characteristic features of the crystal grains themselves which are derived from the halogen compositions and the shapes thereof in the photographic materials.
However, these silver halide emulsions do not always fully satisfy any and every necessary property. Accordingly, improvements for higher sensitivity, better gradation, more excellent storage preservation and processing preservation and more rapid processability are always strived for, and various studies for improvements are being continued. In particular, rapid processability is especially desired in these days, and development of silver halide crystal grains having a higher potential with respect to the above-mentioned points as well as development of chemical sensitization, or spectral sensitization of the crystal grains and, additionally, development of techniques for incorporating the crystal grains in photographic light-sensitive materials are becoming increasingly important. In order to obtain rapid processing, it is important to prevent any fog of silver chloride-containing emulsions and to obtain a stable and excellent gradation without deteriorating the development processability of the photographic materials.